Caption: War Publications - WWI Compilation 1923 - Article 46
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* > plane, comparat i h as the distance from the gun to the baUery-comhiander's station). We have thus the important RULE: J If r and h are both measured in the same unit, then the 1 mils / OCX) 20QO male subtended b\ h in Fig. 2 is h : ( \IOOO (appr.). I [> j A sighting instrument graduated in mils enables an observer to determine immediately each of the quantities r, h, k from the other two. In estimating the error caused by applying the rule stated above, two sources of error must be considered. Firstly, the mil is used as if it ooo per cent. Secondly, we have an error which varies with the angle and which is caused by replacing l:r by h: r. These two errors tend to counteract each other. Therefore the rule gives correct results when the error from the second cause is as large as the error from the first cause, that is, about two per cent. This happens for an angle in the neighborhood of fifteen degrees (about 270 mils), as we know. For this question compare Whit tern ore. PROBLEMS * 3000 yds. distant from the gun and 200 *eet higher than the gun. Find the angle of site. (See Fig. 1). 2. Find the angle of site when (a) range = 2500 yds., target 200 yds. higher than gun (b) range = 4700 yds., target 150 ft. lower than gun. Ans. (b) : — 10.6 mils. gun an angl 3- A tower of 150 ft. height subtend* n ^ils. Find the distance from crun to tower Ans.: About 5000 feet. 4- A tree subtends at a distance of 1500 ft. an angle of 60 mils. Ho w high is the tree ? iding * in the following problems by # 5. Find the error made the rule given in the text. t problems involving the mil 1. 18 Pi
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